A
bstract
The production of dark matter in association with Higgs bosons is predicted in several extensions of the Standard Model. An exploration of such scenarios is presented, considering final ...states with missing transverse momentum and
b
-tagged jets consistent with a Higgs boson. The analysis uses proton-proton collision data at a centre-of-mass energy of 13 TeV recorded by the ATLAS experiment at the LHC during Run 2, amounting to an integrated luminosity of 139 fb
−
1
. The analysis, when compared with previous searches, benefits from a larger dataset, but also has further improvements providing sensitivity to a wider spectrum of signal scenarios. These improvements include both an optimised event selection and advances in the object identification, such as the use of the likelihood-based significance of the missing transverse momentum and variable-radius track-jets. No significant deviation from Standard Model expectations is observed. Limits are set, at 95% confidence level, in two benchmark models with two Higgs doublets extended by either a heavy vector boson
Z
′ or a pseudoscalar singlet
a
and which both provide a dark matter candidate
χ
. In the case of the two-Higgs-doublet model with an additional vector boson
Z
′, the observed limits extend up to a
Z
′ mass of 3 TeV for a mass of 100 GeV for the dark matter candidate. The two-Higgs-doublet model with a dark matter particle mass of 10 GeV and an additional pseudoscalar
a
is excluded for masses of the
a
up to 520 GeV and 240 GeV for tan
β
= 1 and tan
β
= 10 respectively. Limits on the visible cross-sections are set and range from to 0.05 fb to 3.26 fb, depending on the missing transverse momentum and
b
-quark jet multiplicity requirements.
A
bstract
A measurement of prompt photon-pair production in proton-proton collisions at
s
= 13 TeV is presented. The data were recorded by the ATLAS detector at the LHC with an integrated luminosity ...of 139 fb
−
1
. Events with two photons in the well-instrumented region of the detector are selected. The photons are required to be isolated and have a transverse momentum of
p
T
,
γ
1
2
>
40 (30) GeV for the leading (sub-leading) photon. The differential cross sections as functions of several observables for the diphoton system are measured and compared with theoretical predictions from state-of-the-art Monte Carlo and fixed-order calculations. The QCD predictions from next-to-next-to-leading-order calculations and multi-leg merged calculations are able to describe the measured integrated and differential cross sections within uncertainties, whereas lower-order calculations show significant deviations, demonstrating that higher-order perturbative QCD corrections are crucial for this process. The resummed predictions with parton showers additionally provide an excellent description of the low transverse-momentum regime of the diphoton system.
A
bstract
Measurements of four-lepton differential and integrated fiducial cross-sections in events with two same-flavour, opposite-charge electron or muon pairs are presented. The data correspond to ...139 fb
−
1
of
s
= 13 TeV proton-proton collisions, collected by the ATLAS detector during Run 2 of the Large Hadron Collider (2015–2018). The final state has contributions from a number of interesting Standard Model processes that dominate in different four-lepton invariant mass regions, including single
Z
boson production, Higgs boson production and on-shell
ZZ
production, with a complex mix of interference terms, and possible contributions from physics beyond the Standard Model. The differential cross-sections include the four-lepton invariant mass inclusively, in slices of other kinematic variables, and in different lepton flavour categories. Also measured are dilepton invariant masses, transverse momenta, and angular correlation variables, in four regions of four-lepton invariant mass, each dominated by different processes. The measurements are corrected for detector effects and are compared with state-of-the-art Standard Model calculations, which are found to be consistent with the data. The
Z
→ 4
ℓ
branching fraction is extracted, giving a value of (4
.
41 ± 0
.
30) × 10
−
6
. Constraints on effective field theory parameters and a model based on a spontaneously broken
B − L
gauge symmetry are also evaluated. Further reinterpretations can be performed with the provided information.
Background
Some studies have reported that polyamine levels may influence immune system programming. The aim of this study was to evaluate the polyamine profile during gestation and its associations ...with maternal allergy and cytokine production in cord blood cells in response to different allergenic stimuli.
Methods
Polyamines were determined in plasma of pregnant women (24 weeks, N = 674) and in umbilical cord samples (N = 353 vein and N = 160 artery) from the Mediterranean NELA birth cohort. Immune cell populations were quantified, and the production of cytokines in response to different allergic and mitogenic stimuli was assessed in cord blood.
Results
Spermidine and spermine were the most prevalent polyamines in maternal, cord venous, and cord arterial plasma. Maternal allergies, especially allergic conjunctivitis, were associated with lower spermine in umbilical cord vein. Higher levels of polyamines were associated with higher lymphocyte number but lower Th2‐related cells in cord venous blood. Those subjects with higher levels of circulating polyamines in cord showed lower production of inflammatory cytokines, especially IFN‐α, and lower production of Th2‐related cytokines, mainly IL‐4 and IL‐5. The effects of polyamines on Th1‐related cytokines production were uncertain.
Conclusions
Spermidine and spermine are the predominant polyamines in plasma of pregnant women at mid‐pregnancy and also in umbilical cord. Maternal allergic diseases like allergic conjunctivitis are related to lower levels of polyamines in cord vein, which could influence the immune response of the newborn. Cord polyamine content is related to a decreased Th2 response and inflammatory cytokines production, which might be important to reduce an allergenic phenotype in the neonate.
A
bstract
In this paper, a new technique for reconstructing and identifying hadronically decaying
τ
+
τ
−
pairs with a large Lorentz boost, referred to as the di-
τ
tagger, is developed and used for ...the first time in the ATLAS experiment at the Large Hadron Collider. A benchmark di-
τ
tagging selection is employed in the search for resonant Higgs boson pair production, where one Higgs boson decays into a boosted
b
b
¯
pair and the other into a boosted
τ
+
τ
−
pair, with two hadronically decaying
τ
-leptons in the final state. Using 139 fb
−
1
of proton-proton collision data recorded at a centre-of-mass energy of 13 TeV, the efficiency of the di-
τ
tagger is determined and the background with quark- or gluon-initiated jets misidentified as di-
τ
objects is estimated. The search for a heavy, narrow, scalar resonance produced via gluon-gluon fusion and decaying into two Higgs bosons is carried out in the mass range 1–3 TeV using the same dataset. No deviations from the Standard Model predictions are observed, and 95% confidence-level exclusion limits are set on this model.
A
bstract
A search for forward proton scattering in association with light-by-light scattering mediated by an axion-like particle is presented, using the ATLAS Forward Proton spectrometer to detect ...scattered protons and the central ATLAS detector to detect pairs of outgoing photons. Proton-proton collision data recorded in 2017 at a centre-of-mass energy of
s
= 13 TeV were analysed, corresponding to an integrated luminosity of 14.6 fb
−
1
. A total of 441 candidate events were selected. A search was made for a narrow resonance in the diphoton mass distribution, corresponding to an axion-like particle (ALP) with mass in the range 150–1600 GeV. No excess is observed above a smooth background. Upper limits on the production cross section of a narrow resonance are set as a function of the mass, and are interpreted as upper limits on the ALP production coupling constant, assuming 100% decay branching ratio into a photon pair. The inferred upper limit on the coupling constant is in the range 0.04–0.09 TeV
−
1
at 95% confidence level.
A
bstract
A search for a new heavy scalar particle
X
decaying into a Standard Model (SM) Higgs boson and a new singlet scalar particle
S
is presented. The search uses a proton-proton (
pp
) collision ...data sample with an integrated luminosity of 140 fb
−
1
recorded at a centre-of-mass energy of
s
= 13 TeV with the ATLAS detector at the Large Hadron Collider. The most sensitive mass parameter space is explored in
X
mass ranging from 500 to 1500 GeV, with the corresponding
S
mass in the range 200–500 GeV. The search selects events with two hadronically decaying
τ
-lepton candidates from
H
→
τ
+
τ
−
decays and one or two light leptons (
ℓ
=
e
,
μ
) from
S
→
VV
(
V
=
W
,
Z
) decays while the remaining
V
boson decays hadronically or to neutrinos. A multivariate discriminant based on event kinematics is used to separate the signal from the background. No excess is observed beyond the expected SM background and 95% confidence level upper limits between 72 fb and 542 fb are derived on the cross-section
σ
(
pp
→
X
→
SH
) assuming the same SM-Higgs boson-like decay branching ratios for the
S
→
VV
decay. Upper limits on the visible cross-sections
σ
(
pp
→
X
→
SH
→
WWττ
) and
σ
(
pp
→
X
→
SH
→
ZZττ
) are also set in the ranges 3–26 fb and 6–33 fb, respectively.
Searches for long-lived particles (LLPs) are among the most promising avenues for discovering physics beyond the Standard Model at the Large Hadron Collider (LHC). However, displaced signatures are ...notoriously difficult to identify due to their ability to evade standard object reconstruction strategies. In particular, the ATLAS track reconstruction applies strict pointing requirements which limit sensitivity to charged particles originating far from the primary interaction point. To recover efficiency for LLPs decaying within the tracking detector volume, the ATLAS Collaboration employs a dedicated large-radius tracking (LRT) pass with loosened pointing requirements. During Run 2 of the LHC, the LRT implementation produced many incorrectly reconstructed tracks and was therefore only deployed in small subsets of events. In preparation for LHC Run 3, ATLAS has significantly improved both standard and large-radius track reconstruction performance, allowing for LRT to run in all events. This development greatly expands the potential phase-space of LLP searches and streamlines LLP analysis workflows. This paper will highlight the above achievement and report on the readiness of the ATLAS detector for track-based LLP searches in Run 3.
A determination of the jet energy scale is presented using proton–proton collision data with a centre-of-mass energy of
s
=
13
TeV, corresponding to an integrated luminosity of 140 fb
-
1
collected ...using the ATLAS detector at the LHC. Jets are reconstructed using the ATLAS particle-flow method that combines charged-particle tracks and topo-clusters formed from energy deposits in the calorimeter cells. The anti-
k
t
jet algorithm with radius parameter
R
=
0.4
is used to define the jet. Novel jet energy scale calibration strategies developed for the LHC Run 2 are reported that lay the foundation for the jet calibration in Run 3. Jets are calibrated with a series of simulation-based corrections, including state-of-the-art techniques in jet calibration such as machine learning methods and novel in situ calibrations to achieve better performance than the baseline calibration derived using up to 81 fb
-
1
of Run 2 data. The performance of these new techniques is then examined in the in situ measurements by exploiting the transverse momentum balance between a jet and a reference object. The
b
-quark jet energy scale using particle flow jets is measured for the first time with around 1% precision using
γ
+jet events.
A search for the dimuon decay of the Standard Model (SM) Higgs boson is performed using data corresponding to an integrated luminosity of 139 fb−1 collected with the ATLAS detector in Run 2 pp ...collisions at s=13 TeV at the Large Hadron Collider. The observed (expected) significance over the background-only hypothesis for a Higgs boson with a mass of 125.09 GeV is 2.0σ (1.7σ). The observed upper limit on the cross section times branching ratio for pp→H→μμ is 2.2 times the SM prediction at 95% confidence level, while the expected limit on a H→μμ signal assuming the absence (presence) of a SM signal is 1.1 (2.0). The best-fit value of the signal strength parameter, defined as the ratio of the observed signal yield to the one expected in the SM, is μ=1.2±0.6.
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